Mounting frames of this type are needed for example in control panel assemblies, for component racks and holders, in household wiring, for equipment cabinets, and the like. They are conventionally screwed together from perforated angle-profile or U-profile sections, optionally using separate corner connectors. Assembly by means of screwing is rather time-consuming, however, and any protruding nuts and screw heads may limit the use of the mounting frame. Because the profile sections overlap at the corners, they are offset relative to one another and so do not form a flat frame, and protruding corners or edges of the profiles may be dangerous and may also make the frames difficult to use.
In a known arrangement of the above type (Austrian Patent 295,406), two four-sided hollow profiles having the same cross section can be connected to one another at the corners, without overlapping. However, the profiles to be joined are different; one is provided with square windows on all four sides, while the other is provided with a longitudinal slit on one side (the other side is closed). The connector for this includes two blocks, which are longitudinally inserted into the slit profile and can be spread in it by means of a pressure screw. Two sheet- metal tabs, each protruding from one of the blocks at an angle, engage a window of the other profile from the outside. A connection of this kind cannot take significant loads, however, because on the one hand there is virtually only an edge-to-edge contact between the sheet-metal tab and the window, and on the other the connector is only inadequately secured against tension from the spreading in the other profile.